9-Phosphatriptycene Derivatives: From Their Weak Basicity to Their Application in Frustrated Lewis Pair Chemistry

Abstract

The accurate prediction of the basicity of tertiary phosphines in acetonitrile and water is reported by the linear correlation between computed ΔpK a’s obtained by density functional theory (DFT) and experimental values extracted from the literature. This method is applied to the prediction of pK a values of 9-phosphatriptycene derivatives and showed that they are weaker Brønsted bases than their triphenylphosphine analogues. This lower reactivity is attributed to their high pyramidalization that increases their lone pair 3s character, stabilizing its energy level. Their potential application in frustrated Lewis pair chemistry is then considered by investigating the hydrogenation of 1,1-diphenylethylene by the tris­(pentafluorophenyl)­borane/1-chloro-9-phosphatriptycene frustrated Lewis pair.

Frustrated Lewis pair‐catalyzed hydrogenation of unactivated alkenes with sterically hindered 9‐phosphatriptycenes

“…Entry 5 shows that a 9‐phosphatriptycene, even with electron‐donating groups, is still a more potent catalyst for this reaction than triarylphosphines (with activating tolyl, mesityl or deactivating bromine and chlorine substituents, entries 6, 7, 8 and 9 respectively), demonstrating that there is indeed a deactivating effect on the phosphorus reactivity intrinsic to the triptycene scaffold, regardless of additional electronic and steric effects brought by substituents. In addition, the FLP catalysts consisting of BCF and phosphatriptycenes 3 or 5 (p K of −2.6 and +0.2, respectively) [15c] performed better for the hydrogenation of cyclohexene (entry 10) than the FLP catalyst consisting of BCF paired with the commercially available deactivated phosphine P(C 6 F 5 )Ph 2 (p K of +2.6) [10b] which was used for the hydrogenation of more activated olefins or arenes [10a,20] …”

“…Bulkier phosphatriptycenes 4 and 6 on the other hand display highly endergonic values of ΔG 0 adduct , showing no adduct formation. Among these, 1‐chloro‐9‐phosphatriptycene 3 was selected because it displays the highest yield of synthesis and the basicity of the phosphine is further reduced by the chlorine atom [15b,c] . After hydrogen activation with BCF, the phosphonium cation generated will be more acidic than the unsubstituted 9‐phosphatriptycene or derivatives bearing electron‐donating groups, which will favor the protonation of the olefin in the next step of the catalytic cycle.…”

The heterometallic one-dimensional solvated coordination polymer [NiPt2Cl6(TRIP-Py)4] n

“…Accordingly, until our recent publication (Gildenast et al, 2022b), no metal complex with more than two phosphatriptycene ligands bound to a single metal cation had been reported. At the same time, the geometry forces acute C-P-C angles which increases the s-character of the lone pair, lowering its basicity and �-donor strength while increasing the � acidity (Agou et al, 2004;Freijee & Stam, 1980;Jongsma et al, 1974;Drover et al, 2018;Hu et al, 2019;Mahaut et al, 2022). This strengthens the bond, especially towards electron-rich metal cations (Cao et al, 2019;Hu et al, 2021).…”

A Rigid Linker for Site-Selective Coordination of Transition Metal Cations: Combining an Acetylacetone with a Caged Phosphine

“…Recently we approached this issue by introducing the caged phosphine scaffold of the triptycene into CP chemistry . The triptycene scaffold not only gives a rigid linear linker, but it also stabilizes the phosphorus further, making it resistant toward oxidation with ambient oxygen in both solid state and solution. , Furthermore, the geometrical changes induced by the caged scaffold lower the basicity and increase the π-acidity of the phosphorus, strengthening its interaction with soft transition metal cations. − …”